As an audiologist, what is the first thing that comes to your mind when you hear the word autism? I bet that you are imagining a child covering his or her ears in the presence of noise. Many of us have seen patients with autism spectrum disorder (ASD) in our practices.
In addition to hypersensitivity to sound, which some may refer to as hyperacusis, auditory symptoms in the ASD population include tinnitus, inattentiveness to verbal stimuli, selective auditory attention, and atypical performance of the central auditory system.
A recent epidemiological study from Gallaudet Research Institute revealed that one in 59 children with hearing loss were also receiving services for autism—a much higher prevalence than the one in 110 normal hearing children reported to have ASD (J Autism Dev Disord 2012;42:2027-2037 http://link.springer.com/article/10.1007/s10803-012-1452-9).
Several other studies have also demonstrated commonalities between people with hearing loss or deafness and those with autism spectrum disorders (Am Ann Deaf 2009;154:5-14 http://muse.jhu.edu/login?auth=0&type=summary&url=/journals/american_annals_of_the_deaf/v154/154.1.vernon.html; Dev Med Child Neurol 2006;48:85-89 http://onlinelibrary.wiley.com/doi/10.1017/S001216220600020X/full; Child Dev 2005;76:502-517 http://onlinelibrary.wiley.com/doi/10.1111/j.1467-8624.2005.00859.x/abstract).
For example, in a study of 199 children and adolescents with autism, 7.9 percent had mild to moderate hearing impairment, and 3.5 percent had pronounced to profound bilateral hearing loss or deafness (J Autism Dev Disord 1999;29:349-357 http://link.springer.com/article/10.1023/A%3A1023022709710).
Recent research investigating the neuroanatomical diversity and auditory symptoms of autism spectrum disorder holds lessons for the management of patients with ASD in the hearing healthcare clinic.
From a neuroscientific point of view, we can describe autism as a neurodevelopmental disorder with atypical neural connectivity. Rich evidence from the scientific literature and imaging studies suggests differences in brain structures in people with ASD. These differences are in a variety of areas of the brain, and auditory centers are no exceptions.
As audiologists, we are familiar with the role of the superior olivary complex in the process of sound localization. Studies have shown malformation of this lower brainstem area in ASD populations (Brain Res 2011;1398:102-112 http://www.sciencedirect.com/science/article/pii/S0006899311008730; Brain Res 2011;1367:360-371 http://www.sciencedirect.com/science/article/pii/S0006899310022225).
In a study of sound localization abilities, there were no differences in horizontal localization between adults who had ASD and a control group; however, vertical localization was significantly impaired in the ASD group ( J Psychiatry Neurosci 2013;38:398-406 http://jpn.ca/vol38-issue6/38-6-398/). This finding confirms that the ASD population has neuroanatomical changes in the auditory brainstem.
Neuroimaging studies have revealed differences in the brain structures and neurochemistry of people with ASD. For example, voxelwise comparisons have shown increased gray matter volume in the anterior temporal and dorsolateral prefrontal regions in the ASD population ( Arch Gen Psychiatry 2012;69:195-209 http://archpsyc.jamanetwork.com/article.aspx?articleid=1107445).
Advancements in neuroimaging technology and the employment of methods beyond MRI and fMRI, such as diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS), have contributed significantly to the study and analysis of neural diversity in people with ASD.
Neuroimaging studies using these methods have shown differences in a range of brain structures, such as the arcuate fasciculus ( NeuroImage 2010;51:1117-1125 http://www.sciencedirect.com/science/article/pii/S1053811910001059), corpus callosum ( NeuroImage 2007;34:61-73 http://www.sciencedirect.com/science/article/pii/S1053811906008901), and other auditory- and language-related brain structures that may be behind the difficulties processing emotion in others’ voices that's experienced by people with ASD ( Proc Nat Acad Sci U S A 2013;110:12060-12065 http://www.pnas.org/content/110/29/12060.full).
In addition, an MRI study looking at the size of the planum temporale and Heschl's gyrus in children with ASD and typical children indicated larger left planum temporale volume compared with the right in control subjects, but not in children with ASD, and no significant difference in the size of the Heschl's gyrus between the two groups ( J Autism Dev Disord 2005;35:479-486 http://link.springer.com/article/10.1007/s10803-005-5038-7).
The brain's structural diversity has also been investigated in syndromic forms of ASD, like XYY syndrome. In that condition, increased brain matter volume has been reported, which may contribute to the higher frequency of ASD in this population ( Dev Med Child Neurol 2012;54:1149-1156 http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8749.2012.04418.x/full).
In people who have ASD and tuberous sclerosis complex, a genetic disorder resulting in the growth of nonmalignant tumors in the brain and other vital organs, the function of the arcuate fasciculus was diminished, resulting in poor language skills ( Cereb Cortex 2013;23:1526-1532 http://cercor.oxfordjournals.org/content/23/7/1526.full).
MAJOR AUDITORY SYMPTOMS
A few questionnaires are available for the monitoring and assessment of sound hypersensitivity and hyperacusis in the ASD population, such as the Hyperacusis Questionnaire ( ORL J Otorhinolaryngol Relat Spec 2002;64:436-442 http://www.karger.com/Article/FullText/67570) and the recently validated Auditory Behavior Questionnaire ( J Autism Dev Disord 2013;43:978-984 http://link.springer.com/article/10.1007/s10803-012-1626-5).
Previous studies have shown an 18-percent prevalence of hyperacusis in people with autism ( J Autism Dev Disord 1999;29:349-357 http://link.springer.com/article/10.1023/A%3A1023022709710). In our lab, we investigated self-reported hyperacusis and tinnitus in people with Asperger syndrome. Of 55 participants in the study, 38 (69%) reported hyperacusis, and 19 (35%) reported tinnitus (manuscript in preparation).
Another recent study evaluated the relationship between hypersensitivity to sound and superior semicircular canal dehiscence ( Eur Arch Otorhinolaryngol 2013;270:2353-2358 http://link.springer.com/article/10.1007/s00405-013-2482-4). It found that 29 percent of people with ASD who showed hypersensitivity to sound had superior semicircular canal dehiscence, as revealed by CT studies.
As conductive hearing loss is a common finding in children with autism, routine tympanometry and otoacoustic emission (OAE) evaluations should be considered.
Among 100 young people with autism in a recent study, abnormal tympanometric patterns (i.e., types B and C2) and absent OAEs at lower frequencies were significantly more common than in age-matched controls ( Eur J Pediatr 2013;172:1007-1010 http://link.springer.com/article/10.1007/s00431-013-1980-0).
Behavioral evaluations are less reliable in children with autism relative to typically developing children, data have suggested.
For example, in a study of 22 children with autism and 22 age-matched, typically developing children evaluated for hearing, electrophysiological and physiological measures such as auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) showed similar results across both groups; however, behavioral thresholds were worse in the autistic group ( Ear Hear 2006;27:430-441 http://journals.lww.com/ear-hearing/Fulltext/2006/08000/Auditory_Characteristics_of_Children_with_Autism.11.aspx).
These findings emphasize the importance of including electrophysiological evaluation in the hearing test battery of this vulnerable population.
DPOAEs and transient-evoked otoacoustic emissions (TEOAEs) have shown mixed results (e.g., Ear Hear 2006;27:299-312 http://journals.lww.com/ear-hearing/Fulltext/2006/06000/Peripheral_Audition_of_Children_on_the_Autistic.9.aspx; Autism 2007;11:73-79 http://aut.sagepub.com/content/11/1/73.abstract), with several researchers finding no differences between groups with and without autism, and others showing potential differences. However, all these studies concluded that such physiological measures are very important to the study of the integrity of the auditory system in autism.
Research from our laboratory evaluated DPOAE amplitudes in children with autism and a control group, showing reduced DPOAEs in the former group ( Int J Audiol 2012;51:345-352 http://informahealthcare.com/doi/abs/10.3109/14992027.2011.626202). When contralateral suppression was employed, the effect of contralateral noise was not as strong in children with autism as it was in the control group.
These findings of a possible combined effect of recruitment and lack of auditory filter—because of early cochlear dysfunction and efferent system dysfunction, respectively—may explain why children with autism have hypersensitivity to sound.
Interestingly, a similar study in our laboratory detected no significant differences in DPOAE amplitudes or contralateral suppression between 18 boys with Asperger syndrome and an age-matched control group ( Int J Pediatr Otorhinolaryngol 2013;77:947-954 http://www.sciencedirect.com/science/article/pii/S0165587613001146).
Auditory electrophysiological event-related potentials (ERPs) and their magnetic counterparts also have been extensively employed in the study of autism.
A 2011 study showed significantly delayed magnetic mismatch negativity field responses in ASD participants, particularly those with language impairment, leading the authors to speculate that these findings can be used as biomarkers for language impairment and autism ( Biol Psychiatry 2011;70:263-269 http://www.biologicalpsychiatryjournal.com/article/S0006-3223(11)00063-1/abstract).
In terms of balance abnormalities, posturographic evaluation of people with ASD has shown a larger sway on the platform compared with control subjects ( J Autism Dev Disord 2003;33:643-652 http://link.springer.com/article/10.1023/B%3AJADD.0000006001.00667.4c).
Management of auditory complications in the ASD population is multidimensional, addressing hearing loss, auditory processing, hypersensitivity to sound, and tinnitus.
Results from studies looking at the effects of cochlear implants on profoundly deaf children with autism are promising, demonstrating significant improvements in auditory communication following implantation ( Arch Otolaryngol Head Neck Surg 2004;130:666-671 http://archotol.jamanetwork.com/article.aspx?articleid=647549).
FM systems have been shown to be very effective as well, particularly for the enhancement of speech perception in noise ( J Pediatr 2014;164:352-357 http://www.jpeds.com/article/S0022-3476(13)01212-2/abstract; J Commun Disord 2013;46:30-52 http://www.sciencedirect.com/science/article/pii/S0021992412001165).
In ASD, differences in audiovisual integration for speech processing, such as altered neural networks ( Autism Res 2012;5:39-48 http://onlinelibrary.wiley.com/doi/10.1002/aur.231/full), may have implications for rehabilitation and auditory training.
The effects of auditory training and rehabilitative techniques, such as Fast ForWord, have been documented through the use of pre- and post-therapy electrophysiological recordings. Children with autism spectrum disorder had training-related changes in multiple dimensions, such as brainstem and cortical response timing, and pitch-tracking ( Behav Brain Funct 2010;6:60 http://www.behavioralandbrainfunctions.com/content/6/1/60).
Techniques such as neurofeedback, which enables self-regulation of brain oscillations, also have led to improvements in cognitive functioning for children with autism ( Appl Psychophysiol Biofeedback 2013;38:17-28 http://link.springer.com/article/10.1007/s10484-012-9204-3).
There is evidence that the neural network of the auditory pathways reconfigures during neurofeedback ( NeuroImage 2013;81:243-252 http://www.sciencedirect.com/science/article/pii/S1053811913005132), making this approach potentially useful for people with ASD and auditory processing disorders.
Hearing aid fitting protocols and verification practices are pretty similar in ASD and non-ASD populations ( Am J Audiol 2001;10:32-40 http://aja.pubs.asha.org/Article.aspx?articleid=1773863), and management strategies for tinnitus and hyperacusis are also comparable across the two groups.
Techniques such as sound therapy with custom-made sound tracks or ear-level sound generators combined with habituation therapy and counseling have been promising for tinnitus management.
The issue of sound sensitivity is critical. It is believed that sound desensitization is very useful for reducing sound sensitivity. Unfortunately, many people with autism spectrum disorder are equipped with sound-protection devices, such as earplugs. Some parents believe that this kind of protection is helpful and insist on using it.
One of the important steps in sound desensitization, however, is avoiding unnecessary use of sound-protection devices, particularly in environments that are not extraordinarily loud. Acoustical enrichment of the environment with music, musical toys, and computer-generated sounds will expedite the desensitization process.
Some clinicians recommend “breaking” the bond between the auditory and limbic systems that potentially is causing hypersensitivity to sound ( Focus Autism Other Dev Disabl 2011;28:184-186 http://foa.sagepub.com/content/26/3/184.full.pdf). The negative emotional descriptions of loud sounds, such as “scary and fearful sounds,” should be replaced by descriptions such as “unwanted sounds” ( Focus Autism Other Dev Disabl 2011;26:184-186 http://foa.sagepub.com/content/26/3/184.full.pdf+html).
A simple method of sound desensitization is to ask patients or their parents to provide the clinician with a list of sounds that are more annoying than others. The list of annoying sounds may include a fire alarm, flushing toilet, and vacuum cleaner. Most of these sounds can be downloaded as sound files to personal music players.
Patients are instructed to listen to these unwanted sounds at a low level for 15 minutes to 20 minutes a day, slightly increasing the volume every week. This is a very effective method for improving sound tolerance issues in the ASD population.
If necessary, sound tolerance conditions such as misophonia, hyperacusis, recruitment, and phonophobia should be explained to patients and their parents. Furthermore, extensive directive counseling and cognitive behavioral therapy by trained practitioners will ease the process of desensitization to sound.